Nonwoven webs have been used to make a variety of products, which desirably have particular levels of softness, strength, uniformity, liquid handling properties such as absorbency, and other physical properties. Such products include towels, industrial wipes, adult incontinence products, infant care products such as baby diapers, absorbent feminine care products, and garments such as medical apparel, just to name a few products. Nonwoven webs may make up one or more layers in these products. Nonwoven webs have also been used in other applications including as a filter media typically used as fluid filters such as air filters. Nonwoven webs have also been used as sound absorbing materials which are used in vehicles, appliances, homes, and the like.
In the field of filtration, it is desirable to have a filter media which has both high filter efficiency and high fluid (air or liquid) throughput. That is, the filter media must have the ability to prevent fine particles from passing through the filter media while having a low fluid flow resistance. Typically, filter media prevents fine particles from passing through the filter media by mechanically trapping the particles within the fibrous structure of the filter media. In addition, some filter media, in the case of air filtration media, is also electrostatically charged which allows the filter media to electrostatically attract and capture fine particles. Flow resistance is measured in terms of pressure drop or pressure differential across the filter material. A high pressure drop indicates a high resistance to the fluid flow through the filter media, while a low pressure drop indicates a low fluid flow resistance. In addition, the filter media must also exhibit a useful service life which is not too short as to require frequent cleaning or replacement of the filter containing the filter media.
However, these performance requirements for filter media are generally inversely correlated. There is a balance between filter media efficiency, pressure drop across the filter media, and useful life of a filter media. Generally, as is known in the filter media art, increasing the particle capture efficiency by increasing the surface area of the filtration media increases the pressure drop across the filtration media and/or the reduces the useful life of the filter media. It is also pointed out that a high pressure drop across the filter media increases the energy cost to operate the systems using the filters. This is because the pumps or fans designed to move the fluid through the filter media must be run at a higher speed or pressure to achieve the same desired fluid flow when the pressure drop is large.
There is a need in the art for a filtration media which has high filtration efficiency, low pressure drop across the filtration media and a long service life.